Adjusting initial wireless coverage area transmit power based on device altitude

ABSTRACT

In order to provide better wireless service to wireless communication devices (WCDs) at different altitudes (e.g., on different levels of a high-rise structure), a radio access network (RAN) may include antennas that are configured to provide coverage at these different altitudes. The RAN may assign an initial transmit power to a particular WCD based on the particular WCD&#39;s altitude. For instance, if the particular WCD is above a threshold altitude, the RAN may set the initial transmit power to the WCD to a lower value. However, if the WCD is below the threshold altitude, the RAN may set the initial transmit power to the WCD to a higher value, to overcome low-altitude signal obstructions. As a result, RAN and WCD performance may improve.

BACKGROUND

In urban and some suburban environments, the presence of multi-story andhigh-rise buildings makes the deployment of wireless coverage morechallenging. In conventional wireless networks, the antennas thatradiate to define wireless coverage areas are arranged to providewireless coverage at ground level. As a result, wireless communicationdevices (WCDs) on the upper floors of structures may experience poorwireless service. Wireless network providers have attempted to addressthis problem by aiming some antennas at an angle so that a portion ofwireless coverage is provided to WCDs above ground level.

Overview

Equipped with one or more antennas that provide wireless coverage tovarious altitudes, a radio access network (RAN) may use a frequency or aset of frequencies to define a split wireless coverage area. The splitwireless coverage area may include a first sub-area providing wirelesscoverage to WCDs above a threshold altitude and a second sub-areaproviding wireless coverage to WCDs below the threshold altitude.Alternatively or additionally, the RAN may use some frequencies todefine one or more wireless coverage areas that provide wirelesscoverage to WCDs above the threshold altitude and other frequencies todefine one or more wireless coverage areas that provide wirelesscoverage to WCDs below the threshold altitude.

The altitude of a WCD may be determined in various ways. For example,the WCD may include a global positioning system (GPS) receiver, and theWCD may be able to obtain its altitude via GPS, and then report thisaltitude to the RAN. Based on the reported altitude, and possibly otherfactors, such geographical location of the WCD, the RAN may set theforward traffic channel power at which it transmits to the WCD.Particularly, the RAN may set the power at which it initially transmitsto the WCD based on one or more of these factors. As the WCD moves aboutand/or the quality of the WCD's wireless coverage changes, the RAN mayfurther update this initial transmit power.

Accordingly, in an example embodiment, a first initial transmit power ofa first forward traffic channel of a RAN may be set based on a firstaltitude of a first WCD. A second initial transmit power of a secondforward traffic channel of the RAN may be set based on a second altitudeof a second WCD. The second initial transmit power may be different fromthe first initial transmit power. The RAN may begin transmissions to thefirst WCD using the first initial power on the first forward trafficchannel, and the RAN may also begin transmissions to the second WCDusing the second initial power on the second forward traffic channel.

These and other aspects and advantages will become apparent to those ofordinary skill in the art by reading the following detailed description,with reference where appropriate to the accompanying drawings. Further,it should be understood that this overview and other descriptionthroughout this document is merely for purposes of example and is notintended to limit the scope of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a RAN configured to provide wireless services to WCDs, inaccordance with an example embodiment;

FIG. 2 is a high-level diagram of a computing device, in accordance withan example embodiment;

FIG. 3A illustrates a multi-level wireless coverage configuration, inaccordance with an example embodiment;

FIG. 3B illustrates another multi-level wireless coverage configuration,in accordance with an example embodiment; and

FIG. 4 is a flow chart, in accordance with an example embodiment.

DESCRIPTION I. Example Network Architecture

FIG. 1 is a simplified block diagram of a wireless communication system100 in which example embodiments can be employed. WCD 101 maycommunicate over an air interface 103 a with a base transceiver station(BTS) 104, which is, in turn, coupled to or integrated with a basestation controller (BSC) 106. Similarly, WCD 102 may communicate over anair interface 103 b with BTS 104. Transmissions over air interface 103 afrom BTS 104 to WCD 101 and over air interface 103 b from BTS 104 to WCD102 may take place on “forward links” to the WCDs. Conversely,transmissions over air interface 103 a from WCD 101 to BTS 104 and overair interface 103 b from WCD 102 to BTS 104 may take place on “reverselinks” from the WCDs.

BSC 106 may be connected to a mobile switching center (MSC) 108. BSC106, MSC 108, or both, may act to control assignment of air interfacetraffic channels, and may provide access to wireless circuit-switchedservices such as circuit-voice and circuit-data services. In practice, aBSC may serve multiple BTSs, each of which may define one or morewireless coverage areas.

As represented by its connection to public-switched telephone network(PSTN) 112, MSC 108 may also be coupled with one or more other MSCs orother telephony circuit switches, thereby supporting user mobilityacross MSC regions, as well as local and long-distance landlinetelephone services. A home location register (HLR) 110, which may beconnected to MSC 108, may support mobility-related aspects of subscriberservices, including dynamic tracking of subscriber registration locationand verification of service privileges.

As shown, BSC 106 may also be connected with a packet-data serving node(PDSN) 116 by way of a packet control function (PCF) 114. PDSN 116, inturn, may provide connectivity with a packet-switched network 118, suchas the Internet and/or a wireless carrier's private core packet-network.Nodes on network 118 may include, by way of example, an authentication,authorization, and accounting (AAA) server 120, a Mobile InternetProtocol (mobile-IP) home agent (HA) 122, and a remote computer 124.

After acquiring a traffic channel over air interface 103 a, WCD 101 maytransmit a request to PDSN 116 for a connection to the packet datanetwork. Then, following authentication of WCD 101 by AAA server 120,WCD 101 may be assigned an IP address by PDSN 116 or by HA 122, and maythereafter engage in packet-data communications with entities such asremote computer 124. Similar procedures may take place for WCD 102, viaair interface 103 b.

BTS 104, BSC 106, MSC 108, HLR 110, PCF 114, and PDSN 116 may beconsidered to be RAN components. Thus, these components, and anynetwork(s) and/or links connecting these components to one another, maybe referred to as a RAN. However, a RAN may contain more or fewercomponents.

Further, the description of the elements in FIG. 1 is merelyillustrative and should not be interpreted to limit the characteristicsand functions of these devices. Accordingly, it should be understoodthat this and other arrangements and processes described herein are setforth for purposes of example only. Thus, other arrangements andelements (e.g., machines, interfaces, functions, orders of elements,etc.) can be added or used instead and some elements may be omittedaltogether. Further, as in most communication architectures, thoseskilled in the art will appreciate that many of the elements describedherein are functional entities that may be implemented as discretecomponents or in conjunction with other components, in any suitablecombination or location.

II. Example Computing Device

FIG. 2 is a simplified block diagram exemplifying a computing device200. This computing device illustrates one or more of the functionalelements that may be found in a device arranged to operate in accordancewith the embodiments described herein. Thus, computing device 200 mayrepresent the hardware and/or software architecture of any one or moreof BTS 104, BSC 106, MSC 108, and so on. Further, computing device 200may represent the hardware and/or software architecture of a device notshown in FIG. 1 that instructs or controls various elements of wirelesscommunication system 100.

Computing device 200 may include a processor 202, data storage 204,network interface 206, and input/output function 208, all of which maybe coupled by a system bus 210 or a similar mechanism. Processor 202 mayinclude one or more central processing units (CPUs), such as one or moregeneral purpose processors and/or one or more dedicated processors(e.g., application specific integrated circuits (ASICs) or digitalsignal processors (DSPs), etc.).

Data storage 204, in turn, may comprise volatile and/or non-volatiledata storage and can be integrated in whole or in part with processor202. Data storage 204 may store program instructions, executable byprocessor 202, and data that are manipulated by these instructions tocarry out the various methods, processes, or functions described herein.Alternatively, these methods, processes, or functions can be defined byhardware, firmware, and/or any combination of hardware, firmware andsoftware. Therefore, data storage 204 may include a tangible,non-transitory computer-readable medium, having stored thereon programinstructions that, upon execution by one or more processors, causecomputing device 200 to carry out any of the methods, processes, orfunctions disclosed in this specification or the accompanying drawings.

Network interface 206 may take the form of a wireline connection, suchas an Ethernet, Token Ring, or T-carrier connection. Network interface206 may also take the form of a wireless connection, such as Wifi,BLUETOOTH®, or a wide-area wireless connection. However, other forms ofphysical layer connections and other types of standard or proprietarycommunication protocols may be used over network interface 206.Furthermore, network interface 206 may comprise multiple physicalcommunication interfaces.

Input/output function 208 may facilitate user interaction with examplecomputing device 200. Input/output function 208 may comprise multipletypes of input devices, such as a keyboard, a mouse, a touch screen, amicrophone and/or any other device that is capable of receiving inputfrom a user. Similarly, input/output function 208 may comprise multipletypes of output devices, such as a display, printer, one or more lightemitting diodes (LEDs), speaker, or any other device that is capable ofproviding output discernible to a user. Additionally or alternatively,example computing device 200 may support remote access from anotherdevice, via network interface 206 or via another interface (not shown),such an RS-232 or Universal Serial Bus (USB) port.

III. CDMA Communications

The embodiments herein will be described by way of example withreference to Code Division Multiple Access (CDMA) communications.However, it should be understood that these embodiments can employ otherfamilies of protocols now known or developed in the future.

In a CDMA wireless network, each wireless coverage area may employ oneor more frequency bands, typically 1.25 MHz in bandwidth each, and eachwireless coverage area may be distinguished from adjacent wirelesscoverage areas by a pseudo-random number offset (“PN offset”). Further,each wireless coverage area may concurrently communicate on multiplechannels that are distinguished from one another by different CDMA codes(i.e., different Walsh codes). When a WCD operates in a given wirelesscoverage area, communications between the WCD and the BTS of thewireless coverage area may be carried on a given frequency and may alsobe encoded (e.g., modulated) by the wireless coverage area's PN offsetand a particular Walsh code.

Air interface communications in a wireless coverage area may be dividedinto forward link communications and reverse link communications. On theforward link, certain Walsh codes may be reserved for defining controlchannels, including a pilot channel, a sync channel, and one or morepaging channels, and the remainder may be assigned dynamically for useas traffic channels, i.e., to carry bearer data such as email, webbrowsing, voice, video, and so on. Similarly, on the reverse link, oneor more offsets of a CDMA code (i.e., offsets of a PN long code) may bereserved for defining control channels, such as access channels, and theremaining offsets may be assigned dynamically to WCDs for use as trafficchannels.

In order to acquire the signals of a wireless coverage area, a WCD maybe configured by its home wireless service provider with a preferredroaming list (PRL) of frequencies to scan when the WCD is seekingservice. The frequencies in the PRL may be arranged in a listed order,and the WCD may be arranged to scan the frequencies in the order listedin the PRL, starting with the first-listed frequency. If the WCD cannotreceive a signal on the first-listed frequency at sufficient signalstrength, the WCD may then scan the next frequency in the PRL. Thisprocess may continue until the WCD discovers that it can receive afrequency with a sufficiently strong signal, or the WCD reaches the endof the PRL.

Once a WCD acquires a wireless coverage area on a particular frequency,the WCD may then receive information about the configuration of thewireless coverage area from one or more of the wireless coverage area'spilot channel, sync channel, and paging channel. Upon acquiring thewireless coverage area, the WCD may be considered to be “idle,” in thatthe WCD is not exchanging bearer data with a BTS. Such an idle WCD maylisten to the paging channel of the primary wireless coverage area forincoming call indications, and other information, from the RAN. The RANmay transmit system parameter messages and/or neighbor list messages tothe WCD via this primary paging channel. These messages may contain PNoffsets of the pilot channels emitted by BTSs that define neighboringwireless coverage areas (e.g., wireless coverage areas defined by theRAN's BTSs or wireless coverage areas defined by nearby BTSs indifferent RANs). An idle WCD may measure the pilot channel signalstrength that it receives from each of these neighboring wirelesscoverage areas.

If, for some period of time, WCD receives pilot channel signals from aneighboring wireless coverage area at a greater strength than the WCDreceives pilot channel signals from the primary wireless coverage area,the WCD may hand off to the neighboring wireless coverage area. To doso, the WCD may stop listening to the primary wireless coverage area'spaging channel and register with the neighboring wireless coverage area.Accordingly, the WCD may begin listening to the neighboring wirelesscoverage area's paging channel, and may transmit a radio environmentreport message to the RAN, via the neighboring wireless coverage area'saccess channel, indicating the handoff. In this way, the neighboringwireless coverage area becomes the WCD's new primary wireless coveragearea.

When the WCD engages in a voice or data call, the WCD may use theprimary wireless coverage area's paging channel and access channel toestablish the call. For example, when an idle WCD originates a newoutgoing call (i.e., the WCD is the caller), the WCD may transmit one ormore access probe (or origination) messages to the RAN via the accesschannel of the primary wireless coverage area. Each access probe messagemay contain an identification of the WCD seeking to establish the call,as well as information specific to the nature of the request, such asthe type of call or session being sought, among other possible details.

The RAN may respond to an access probe message by assigning one or moretraffic channels from one or more wireless coverage areas to the WCD. Tothat end, the RAN may transmit, via the paging channel, an indication ofthe channel assignment (e.g., by identifying frequencies, PN offsets,and/or Walsh codes of the assigned traffic channel(s)). Thistransmission may take the form of one or more channel assignmentmessages directed to the WCD. Then, the now-active WCD (i.e., the WCD isno longer “idle”) may use the assigned traffic channels for transmittingand/or receiving bearer data for the voice or data call.

A WCD may communicate via a number of “active” wireless coverage areasat the same time. Depending on the type and/or configuration of the RAN,the number of active wireless coverage areas may be from one to six.However, more than six active wireless coverage areas may be usedwithout departing from the scope of the embodiments herein. The WCD maymaintain a list of the active wireless coverage areas, which may beidentified according to their PN offsets. This list may be referred toas the WCD's “active set.”

A RAN may be arranged to transmit the same bearer data to a given WCDconcurrently via some or all of the wireless coverage areas in the givenWCD's active set, encoding each transmission according to the PN offsetof the respective wireless coverage area and the Walsh code for theassigned channel therein. Correspondingly, the WCD may decode forwardlink transmissions from each wireless coverage area using the respectivewireless coverage area's PN offset together with the WCD's respectivelyallocated Walsh code for the wireless coverage area. The concurrenttransmissions in wireless coverage areas of the active set provides anadded level of reliability to communications, as well as possiblyincreased quality owing to improved signal-to-noise characteristics. Theconcurrency also facilitates a form of seamless handoff between wirelesscoverage areas, referred to as “soft handoff” when the handoff isbetween wireless coverage areas of different BTSs, and “softer handoff”when the handoff is between wireless coverage areas of the same BTS.

Regularly, or from time to time, the WCD may measure the signal-to-noiseratio (SNR) of a channel (e.g., a pilot channel) from each of thesewireless coverage areas, to determine the respective received signalstrengths of each wireless coverage area. When the WCD determines thatthe received signal strength of its serving wireless coverage area hasdropped below a signal-strength threshold, or the received signalstrength of another wireless coverage area in the active set exceedsthat of the serving wireless coverage area by some amount, the WCD mayrequest a handoff from the serving wireless coverage area to a wirelesscoverage area from which the WCD has received a higher signal strength.Additionally, the WCD may add or remove wireless coverage areas from theactive set based on these signal strengths or for other reasons.

IV. Serving WCDs at a Range of Altitudes

Conventional wireless communication networks are designed to serve WCDsat ground level, in that the antennas that radiate to define wirelesscoverage areas are typically configured to provide most or all of theircoverage at the ground level. However, in urban and even some suburbanenvironments, WCDs may be at various altitudes. For instance, a WCD in askyscraper may be 1,000 feet or more above the ground. As a result, thisWCD may experience poor wireless coverage, or no wireless coverage atall.

In order to address this problem, some BTSs may contain, or beassociated with, one or more antennas that provide wireless coverage athigher altitudes. In possible embodiments, these antennas may be tilted,angled, or otherwise configured, to provide wireless coverage directedto the higher floors of nearby structures.

A. Example Antenna Configurations

FIG. 3A illustrates such a configuration. BTS 300 may include antennas302 and 304. Antenna 302 may radiate to define wireless coverage area306, and also may be configured to aim this coverage toward the higherfloors of multi-story structure 310. Antenna 304 may radiate to definewireless coverage area 308, and also may be configured to aim thiscoverage toward the lower floors of multi-story structure 310.

As shown in FIG. 3A, the antennas may define both wireless coverage area306 and wireless coverage area 308 using the same frequency, frequencyF1. However, a fixed amount of power may be available to define thesewireless coverage areas. Thus, the forward transmit power used byantenna 302 and antenna 304 may be divided by power splitter 312. Forexample, 70% of the forward transmit power may be used to definewireless coverage area 308 and 30% of the forward transmit power may beused to define wireless coverage area 306. In another exampleconfiguration, 50% of the forward transmit power may be used to definewireless coverage area 308 and 50% of the forward transmit power may beused to define wireless coverage area 306.

Other distributions of forward transmit power between the wirelesscoverage areas may be possible. In some embodiments, wireless coverageareas formed in this fashion may be referred to as “sub-areas” of thesame split wireless coverage area.

FIG. 3B illustrates an alternate embodiment in which antenna 302radiates on frequency F1 to define wireless coverage area 306 andantenna 304 radiates on frequency F2 to define wireless coverage area308. Thus, in this embodiment, some frequencies may serve WCDs at higheraltitudes while other frequencies may serve WCDs at lower altitudes.Also, power splitter 312 is replaced by frequency splitter 314.Frequency splitter 314 may contain, for instance, one or more filtersthat direct specific frequency ranges to particular antennas.

In this embodiment, the wireless coverage areas may be defined using thesame or a similar amount of power. In further embodiments, a single BTSmay include both a power splitter and a frequency splitter, andtherefore may provide multi-level wireless coverage on the samefrequencies, but at different powers, while also providing wirelesscoverage to each level using different frequencies at each level.

In FIGS. 3A and 3B, the size and shape of antennas 302 and 304 areexaggerated for purposes of illustration. In practical deployments,antennas may take on various shapes, sizes, and arrangements.

More generally, the entire BTS, antenna, and wireless coverageconfigurations illustrated by FIGS. 3A and 3B are examples. Otherconfigurations are included within the scope of this disclosure. Forinstance, some configurations may include multiple BTSs, and each BTSmay include more than two antennas. Thus, each BTS may define more thantwo wireless coverage areas. For instance, one BTS may include antennassuch that the BTS defines multiple wireless coverage areas that serveWCDs on the higher floors of multi-story structure 310, and multiplewireless coverage areas that serve WCDs on the lower floors ofmulti-story structure 310.

Alternatively or additionally, a BTS may include several antennas thateach serve WCDs on a specific range of floors of multi-story structure310. For instance, multi-story structure 310 may include more than justthe three floors illustrated in FIGS. 3A and 3B. Therefore, one antennamay be aimed to provide wireless coverage to floors one through five,another antenna may be aimed to provide wireless coverage to floors sixthrough ten, and yet another antenna may be aimed to provide wirelesscoverage to floors eleven through fifteen, and so on. Moreover, powersplitter 312 and/or frequency splitter 314 may be part of BTS 300 (e.g.,mounted on BTS 300) rather than a separate component.

The various wireless coverage areas defined by BTS 300 may overlap tosome extent. Thus, a WCD in multi-story structure 310 may be able to beserved by either or both of these wireless coverage areas. For instance,a WCD served by wireless coverage area 306 may be able to receivesignals from wireless coverage area 308, and vice versa.

It should be clear from the preceding discussion that the multi-levelwireless coverage contemplated by FIGS. 3A and 3B could be used to serveWCDs in an urban environment, a suburban environment, and/or any otherenvironment in which WCDs may be at various altitudes. In the following,for purposes of simplicity, it will be assumed that in exampleembodiments only two levels of wireless coverage are provided: one forWCDs above a threshold altitude and another for WCDs below the thresholdaltitude. Nonetheless, any embodiments described herein may begeneralized to support multiple levels of wireless coverage at variousaltitudes.

B. Determining WCD Altitude

One potential aspect of the embodiments described herein involvesdetermining a WCD's altitude, and performing various functions, methods,and/or procedures based on this determined altitude. For example, if aWCD is above a threshold altitude, and therefore better served bywireless coverage areas serving higher altitudes, the RAN and/or the WCDmay behave in a particular fashion. However, if the WCD is below thethreshold altitude, and therefore better served by wireless coverageareas serving lower altitudes, the RAN and/or the WCD may behave in adifferent fashion.

Various techniques may be employed to determine a WCD's altitude. Insome embodiments, a WCD may be equipped with a GPS receiver. Thus, theWCD may be able to obtain its altitude via GPS, and the WCD may reportthis altitude to the RAN. In other embodiments, the WCD may be equippedwith an accelerometer, a gyroscope, and/or an altimeter, and the WCD maybe able to obtain or infer its altitude from measurements performed byone or more of these components. In yet other embodiments, the WCD'saltitude may be determined based on the wireless coverage areas fromwhich the WCD receives signals at or above a threshold signal strength.

Particularly, and as noted above, a WCD may measure the signal strengththat it receives from various wireless coverage areas (e.g., the pilotsignal strengths of these wireless coverage areas). Wireless signalsreceived by WCDs at higher altitudes may be subject to lessinterference, attenuation, and/or distortion than wireless signalsreceived by WCDs at lower altitudes. For example, a WCD at or near thetop of a tall building may be able to receive signals from distant BTSs,at least in part because there is less likely to be physical barriersbetween those BTSs and the WCD. On the other hand, a WCD at or nearground level in an urban or suburban area may be partially or fullysurrounded by buildings, walls, or other structures that could obstructwireless signals from the BTSs. As result, a WCD's altitude may be ableto be determined based on the strength at which the WCD receives signalsfrom distant BTSs.

For purposes of example, Table 1 provides a hypothetical configurationof wireless coverage areas at various distances from a BTS serving WCD 1and WCD 2. WCD 1 is at an altitude of 500 feet, while WCD 2 is at analtitude of 3 feet. Thus, WCD 2 is essentially at ground-floor level.Wireless coverage area PN1 is defined 0.7 miles from the BTS, and itssignals are received at a strength of −6 dB by WCD 1 and −4 dB by WCD 2,respectively. Wireless coverage area PN2 is defined 1.5 miles from theBTS, and its signals are received at a strength of −8 dB by WCD 1 and −8dB by WCD 2, respectively. Wireless coverage area PN3 is defined 4.0miles from the BTS, and its signals are received at a strength of −12 dBby WCD 1 and −14 dB by WCD 2, respectively. Wireless coverage area PN4is defined 5.2 miles from the BTS, and its signals are received at astrength of −13 dB by WCD 1. WCD 2 receives signals from wirelesscoverage area PN4 at a negligible strength or not at all. Thus, WCD 1,which is at a relatively high altitude, can receive signals from themore distant wireless coverage areas at a greater signal strength thanWCD 2.

TABLE 1 Wireless Distance Received Signal Received Signal Coverage fromStrength at WCD 1 Strength at WCD 2 Area BTS (altitude of 500 feet)(altitude of 3 feet) PN1 0.7 miles  −6 dB  −4 dB PN2 1.5 miles  −8 dB −8 dB PN3 4.0 miles −12 dB −14 dB PN4 5.2 miles −13 dB N/A

In some embodiments, the RAN may define a threshold distance from theBTS, beyond which a wireless coverage area is deemed to be “distant.”For instance, this threshold distance for the hypothetical configurationof Table 1 may be 3.5 miles. Thus, wireless coverage areas PN1 and PN2would not be considered distant, while wireless coverage areas PN3 andPN4 would be considered distant. Given this example threshold distance,and the associated grouping of wireless coverage area PN1 with wirelesscoverage area PN2, and wireless coverage area PN3 with wireless coveragearea PN4, the RAN may classify WCD 1 as “high altitude,” because WCD 1can receive signals from both wireless coverage areas PN3 and PN4.Conversely, the RAN may classify WCD 2 as “low altitude” because WCD 2cannot receive signals from wireless coverage area PN4.

More generally, the altitude of a WCD may be determined based on the WCDreporting that it has received signals above a threshold strength fromat least n of the distant wireless coverage areas. Suppose that, for thehypothetical configuration of Table 1, the threshold strength is −13.5dB and n is two. Then the RAN may classify WCD 1 as “high altitude,”because WCD 1 receives signals above a strength of −13.5 dB from distantwireless coverage areas PN3 and PN4. However, the RAN may classify WCD 2as “low altitude,” because WCD 2 does not receive signals above astrength of −13.5 dB from at least two distant wireless coverage areas.

While the discussion above refers to a RAN determining WCD altitude,another device that is not a RAN component may determine WCD altitudeinstead. For instance, WCDs might directly or indirectly transmit theirreports of measured signal strength to one or more server devices, andthese server devices may determine each WCD's respective altitude. Theserver devices may also transmit the determined altitudes to the RAN, orinstruct the RAN to carry out particular functions based on thedetermined altitudes.

Additionally, while just two different classifications of WCD altitude(“high altitude” and “low altitude,” respectively) were discussed inthis section, the methods, processes, and functions described herein maybe generalized to support more than two classifications of WCD altitude.For example, the RAN (or a separate server device) may classify WCDaltitude into several overlapping or non-overlapping altitude ranges.

Furthermore, in addition to GPS, accelerometer, gyroscope, altimeter,and/or signal strength measurements, other ways of determining WCDaltitude may also be possible.

V. Setting Initial Transmit Power Based on Device Altitude

When a RAN assigns a forward traffic channel to a WCD, the RAN maydetermine an initial power that it will use to transmit to the WCD onthe assigned channel. In some embodiments, this initial transmit powermay be based on the WCD's altitude.

For instance, and as noted above, wireless signals received by WCDs athigher altitudes may be subject to less interference, attenuation,and/or distortion than wireless signals received by WCDs at loweraltitudes. Consequently, the RAN may be able to use less forward channelpower to effectively communicate with higher-altitude WCDs than withlower-altitude WCDs. On the other hand, the distance between the RAN'santenna(s) and a very high altitude WCD (such as a WCD at or near thetop of a skyscraper), may be such that the WCD receives wireless signalsfrom the RAN at a reduced strength.

TABLE 2 WCD Initial Forward Altitude (feet) Transmit Power (Watts) x ≦50 4 50 < x ≦ 250 2 250 < x ≦ 500 3 x > 500 4

Consequently, the RAN may set initial forward traffic channel power to aparticular WCD based, at least in part, on the particular WCD'saltitude. In some embodiments, the RAN may contain, or have access to, atable such as Table 2, or equivalents thereof. Table 2 provides a numberof initial forward transmit powers based on WCD altitude.

According to Table 2, for a WCD with an altitude that is less than orequal to 50 feet, the RAN may set the initial forward transmit power tothis WCD to 4 Watts. For a WCD with an altitude that is greater than 50feet and less than or equal to 250 feet, the RAN may set the initialforward transmit power to this WCD to 2 Watts. For a WCD with analtitude that is greater than 250 feet and less than or equal to 500feet, the RAN may set the initial forward transmit power to this WCD to3 Watts. For a WCD with an altitude that is greater than 500 feet, theRAN may set the initial forward transmit power to this WCD to 4 Watts.

The structure of Table 2 is presented for purposes of illustration.Therefore, varying initial transmit powers based on WCD altitude mayrepresented in other ways. Further, the values in Table 2 are mereexamples. Different WCD altitude ranges and different initial forwardtransmit powers may be used. For instance, initial transmit powers tolow-altitude WCDs may be lower than initial transmit powers tohigh-altitude WCDs. Also, these values may be represented in differentunits. Thus, WCD altitude could be measured in meters, initial forwardtransmit power could be measured in kilowatts, and so on.

In addition to setting the initial forward transmit power to a WCD basedon the WCD's altitude, the RAN may also consider the WCD's geographiclocation, including any known barriers between the RAN and the WCD thatcould attenuate signals from the RAN to the WCD. For instance, if theRAN determines that there is a barrier between the WCD and theantenna(s) serving the WCD that could attenuate the RAN signals to theWCD, the RAN may increase the initial forward transmit power to the WCD.

VI. Example Methods

FIG. 4 is a flow chart of an example method. One or more of the steps ofFIG. 4 may be carried out by a RAN component and/or by a computingdevice that is not part of a RAN.

At step 400, a first initial transmit power of a first forward trafficchannel of a RAN may be set based on a first altitude of a first WCD. Atstep 402, a second initial transmit power of a second forward trafficchannel of the RAN may be set based on a second altitude of a secondWCD. The second initial transmit power may be different from the firstinitial transmit power. For instance, the second initial transmit powermay be higher or lower than the first initial transmit power.

In some embodiments, the RAN may define a split wireless coverage areaincluding a first sub-area serving a first set of WCDs that are above athreshold altitude and a second sub-area serving a second set of WCDsthat are below the threshold altitude. Thus, setting the first initialtransmit power based on the first altitude may involve determining thatthe first WCD is in the first set. Similarly, setting the second initialtransmit power based on the second altitude may involve determining thatthe second WCD is in the second set.

Determining that the first WCD is in the first set may involve receivingan indication of the first altitude from the first WCD. Likewise,determining that the second WCD is in the second set may involvereceiving an indication of the second altitude from the second WCD.

Alternatively or additionally, determining that the first WCD is in thefirst set may involve obtaining a first report of signal strengthsreceived by the first WCD. Each signal strength in the first report maybe associated with a respective wireless coverage area. Based on thefirst report of signal strengths received by the first WCD, the firstaltitude may be estimated. Also, determining that the second WCD is inthe second set may involve obtaining a second report of signal strengthsreceived by the second WCD. Each signal strength in the second reportmay be associated with a respective wireless coverage area. Based on thesecond report of signal strengths received by the second WCD, the secondaltitude may be estimated.

In some embodiments, the first report of signal strengths received bythe first WCD may indicate that the first WCD receives, from at least nwireless coverage areas, signals with strengths that are above athreshold signal strength. Similarly, the second report of signalstrengths received by the second WCD may indicate that the second WCDdoes not receive, from at least n wireless coverage areas, signals withstrengths that are above the threshold signal strength.

At step 404, the RAN may begin transmissions to the first WCD. Thetransmissions to the first WCD may use the first initial power on thefirst forward traffic channel. At step 406, the RAN may begintransmissions to the second WCD. The transmissions to the second WCD mayuse the second initial power on the second forward traffic channel.

It should be understood that FIG. 4 depicts a non-limiting embodiment.Thus, more or fewer steps than shown in FIG. 4 may be used withoutdeparting from the scope of the embodiment. Additionally, each of thesesteps may be repeated one or more times, or may be omitted altogether,and these steps may occur in a different order than shown in FIG. 4.

A step or block in any figure herein representing a processing ofinformation may correspond to circuitry that can be configured toperform the specific logical functions of a herein-described method ortechnique. Alternatively or additionally, a step or block thatrepresents a processing of information may correspond to a module, asegment, or a portion of program code (including related data). Theprogram code may include one or more instructions executable by aprocessor for implementing specific logical functions or actions in themethod or technique. The program code and/or related data may be storedon any type of tangible, non-transitory computer-readable medium such asa storage device including computer memory, a disk or hard drive, orother storage media. Thus, the program code may be stored on and/orexecuted by, for example, computing device 200.

Additionally, any enumeration of elements, blocks, or steps in thisspecification or the claims is for purposes of clarity. Thus, suchenumeration should not be interpreted to require or imply that theseelements, block, or steps adhere to a particular arrangement or becarried out in a particular order.

VII. Conclusion

Example embodiments have been described above. Those skilled in the artwill understand, however, that changes and modifications may be made tothese embodiments without departing from the true scope and spirit ofthe invention, which is defined by the claims.

The invention claimed is:
 1. A method comprising: setting a firstinitial transmit power of a first forward traffic channel of a radioaccess network (RAN) based on a first altitude of a first wirelesscommunication device (WCD); setting a second initial transmit power of asecond forward traffic channel of the RAN based on a second altitude ofa second WCD, wherein the second initial transmit power is differentfrom the first initial transmit power; the RAN beginning transmissionsto the first WCD, wherein the transmissions to the first WCD use thefirst initial power on the first forward traffic channel; and the RANbeginning transmissions to the second WCD, wherein the transmissions tothe second WCD use the second initial power on the second forwardtraffic channel.
 2. The method of claim 1, wherein the RAN defines asplit wireless coverage area comprising a first sub-area serving a firstset of WCDs that are above a threshold altitude and a second sub-areaserving a second set of WCDs that are below the threshold altitude,wherein setting the first initial transmit power based on the firstaltitude comprises determining that the first WCD is in the first set,and wherein setting the second initial transmit power based on thesecond altitude comprises determining that the second WCD is in thesecond set.
 3. The method of claim 2, wherein determining that the firstWCD is in the first set comprises receiving an indication of the firstaltitude from the first WCD, and wherein determining that the second WCDis in the second set comprises receiving an indication of the secondaltitude from the second WCD.
 4. The method of claim 2, whereindetermining that the first WCD is in the first set comprises: obtaininga first report of signal strengths received by the first WCD, whereineach signal strength in the first report is associated with a respectivewireless coverage area; and based on the first report of signalstrengths received by the first WCD, estimating the first altitude. 5.The method of claim 4, wherein determining that the second WCD is in thesecond set comprises: obtaining a second report of signal strengthsreceived by the second WCD, wherein each signal strength in the secondreport is associated with a respective wireless coverage area; and basedon the second report of signal strengths received by the second WCD,estimating the second altitude.
 6. The method of claim 5, wherein thefirst report of signal strengths received by the first WCD indicatesthat the first WCD receives, from at least n wireless coverage areas,signals with strengths that are above a threshold signal strength. 7.The method of claim 6, wherein the second report of signal strengthsreceived by the second WCD indicates that the second WCD does notreceive, from at least n wireless coverage areas, signals with strengthsthat are above the threshold signal strength.
 8. A computing devicecomprising: a processor; data storage; and program instructions, storedin the data storage that, upon execution by the processor, cause thecomputing device to (i) set a first initial transmit power of a firstforward traffic channel of a radio access network (RAN) based on a firstaltitude of a first wireless communication device (WCD), (ii) set asecond initial transmit power of a second forward traffic channel of theRAN based on a second altitude of a second WCD, wherein the secondinitial transmit power is different from the first initial transmitpower, (iii) instruct the RAN to begin transmissions to the first WCD,wherein the transmissions to the first WCD use the first initial poweron the first forward traffic channel, and (iv) instruct the RAN to begintransmissions to the second WCD, wherein the transmissions to the secondWCD use the second initial power on the second forward traffic channel.9. The computing device of claim 8, wherein the RAN defines a splitwireless coverage area comprising a first sub-area serving a first setof WCDs that are above a threshold altitude and a second sub-areaserving a second set of WCDs that are below the threshold altitude,wherein setting the first initial transmit power based on the firstaltitude comprises determining that the first WCD is in the first set,and wherein setting the second initial transmit power based on thesecond altitude comprises determining that the second WCD is in thesecond set.
 10. The computing device of claim 9, wherein determiningthat the first WCD is in the first set comprises receiving an indicationof the first altitude from the first WCD, and wherein determining thatthe second WCD is in the second set comprises receiving an indication ofthe second altitude from the second WCD.
 11. The computing device ofclaim 9, wherein determining that the first WCD is in the first setcomprises: obtaining a first report of signal strengths received by thefirst WCD, wherein each signal strength in the first report isassociated with a respective wireless coverage area; and based on thefirst report of signal strengths received by the first WCD, estimatingthe first altitude.
 12. The computing device of claim 11, whereindetermining that the second WCD is in the second set comprises:obtaining a second report of signal strengths received by the secondWCD, wherein each signal strength in the second report is associatedwith a respective wireless coverage area; and based on the second reportof signal strengths received by the second WCD, estimating the secondaltitude.
 13. The computing device of claim 12, wherein the first reportof signal strengths received by the first WCD indicates that the firstWCD receives, from at least n wireless coverage areas, signals withstrengths that are above a threshold signal strength.
 14. The computingdevice of claim 13, wherein the second report of signal strengthsreceived by the second WCD indicates that the second WCD does notreceive, from at least n wireless coverage areas, signals with strengthsthat are above the threshold signal strength.
 15. An article ofmanufacture including a non-transitory computer-readable medium, havingstored thereon program instructions that, upon execution by a computingdevice, cause the computing device to perform operations comprising:setting a first initial transmit power of a first forward trafficchannel of a radio access network (RAN) based on a first altitude of afirst wireless communication device (WCD); setting a second initialtransmit power of a second forward traffic channel of the RAN based on asecond altitude of a second WCD, wherein the second initial transmitpower is different from the first initial transmit power; instructingthe RAN to begin transmissions to the first WCD, wherein thetransmissions to the first WCD use the first initial power on the firstforward traffic channel; and instructing the RAN to begin transmissionsto the second WCD, wherein the transmissions to the second WCD use thesecond initial power on the second forward traffic channel.
 16. Thearticle of manufacture of claim 15, wherein the RAN defines a splitwireless coverage area comprising a first sub-area serving a first setof WCDs that are above a threshold altitude and a second sub-areaserving a second set of WCDs that are below the threshold altitude,wherein setting the first initial transmit power based on the firstaltitude comprises determining that the first WCD is in the first set,and wherein setting the second initial transmit power based on thesecond altitude comprises determining that the second WCD is in thesecond set.
 17. The article of manufacture of claim 16, whereindetermining that the first WCD is in the first set comprises receivingan indication of the first altitude from the first WCD, and whereindetermining that the second WCD is in the second set comprises receivingan indication of the second altitude from the second WCD.
 18. Thearticle of manufacture of claim 16, wherein determining that the firstWCD is in the first set comprises: obtaining a first report of signalstrengths received by the first WCD, wherein each signal strength in thefirst report is associated with a respective wireless coverage area; andbased on the first report of signal strengths received by the first WCD,estimating the first altitude.
 19. The article of manufacture of claim18, wherein determining that the second WCD is in the second setcomprises: obtaining a second report of signal strengths received by thesecond WCD, wherein each signal strength in the second report isassociated with a respective wireless coverage area; and based on thesecond report of signal strengths received by the second WCD, estimatingthe second altitude.